Network Working Group M. West Internet-Draft Google, LLC. Intended status: Informational 21 November 2024 Expires: 25 May 2025 An HTTP Message Signature Profile for Client-Side Verification draft-west-sri-signature-profile-latest Abstract An HTTP Message Signature profile that specifies the requirements for signatures intended as proofs of integrity/provenance that can be enforced upon by clients without any pre-existing relationship to the server which delivered them. About This Document This note is to be removed before publishing as an RFC. The latest revision of this draft can be found at https://mikewest.github.io/rfc9421-sri-profile/draft-west-sri- signature-profile.html. Status information for this document may be found at https://datatracker.ietf.org/doc/draft-west-sri-signature- profile/. Source for this draft and an issue tracker can be found at https://github.com/mikewest/rfc9421-sri-profile. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on 25 May 2025. Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction 2. Conventions and Definitions 3. The SRI Profile 3.1. Components and Parameters: 3.2. Structured Field Types 3.3. Retrieving the Key Material 3.4. Signature Algorithms 3.5. Determine Key/Algorithm Appropriateness 3.6. Derivation Context 3.7. Error Reporting from Verifier to Signer 4. Security Considerations 5. IANA Considerations 6. References 6.1. Normative References 6.2. Informative References Acknowledgments Author's Address 1. Introduction This document defines an HTTP Message Signature profile that specifies the requirements for signatures intended as proofs of integrity/provenance that can be enforced upon by clients without any pre-existing relationship to the server which delivered them. This requires locking down the components and properties of the signature itself, as well as some of the decision points available during the generation of the signature base (Section 2.5 of [RFC9421]). In short: this profile supports only Ed25519 signatures, requires that the public key portion of the verification key material be included in the signature's input, and specifies the ordering of the components and properties to remove potential ambiguity about the signature's construction. 2. Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 3. The SRI Profile The following requirements define a profile of HTTP Message Signatures that enables clients to verify a response's signature without any additional information, following the guidelines laid out in Section 1.4 of [RFC9421]: 3.1. Components and Parameters: The signature's input MUST: 1. Include the following component identifiers (Section 2 of [RFC9421]) with their associated constraints: * identity-digest, which MUST include the sf parameter (Section 2.1 of RFC9421}}) and no other parameters. 2. Include the following parameters (Section 2.3 of [RFC9421]) with their associated constraints: * alg, whose value MUST be the string ed25519 * keyid, whose value MUST be a string containing an base64-encoding of the public key portion of the signature's verification key material. * tag, whose value MUST be the string sri (or something more specific? enforce-ed25519-provenance?) 3. Order the signature's parameters alphabetically. The signature's input MAY: 1. Include the following parameters, with their associated constraints: * created, an integer whose value MUST represent a time in the past. * expires, an integer whose value MUST represent a time in the future. 3.2. Structured Field Types The identity-digest component references the Identity-Digest header defined in [I-D.pardue-http-identity-digest]. It is expected to be a Dictionary Structured Field (Section 3.2 of [STRUCTURED-FIELDS]). 3.3. Retrieving the Key Material The public key of the verification key material can be directly extracted from the signature input's keyid parameter, where it's represented as a base64-encoded string (Section 4 of [RFC4648]). 3.4. Signature Algorithms The only signature algorithm allowed is ed25519. 3.5. Determine Key/Algorithm Appropriateness Since the only accepted algorithm is ed25519, it is appropriate for any context in which this profile will be used, and we require it to be specified as the alg parameter to the signature's input. 3.6. Derivation Context The context for derivation of message components from an HTTP message and its application context is the HTTP message itself, encompassing the response with which the signature was delivered, and the request to which it responds. 3.7. Error Reporting from Verifier to Signer No error reporting is required. Clients MUST represent verification failures as network errors, consistent with [FETCH]'s handling of other server-specified constraints on the usage of response data. 4. Security Considerations This profile has no security considerations beyond those specified in [RFC9421] itself, and in [SIGSRI] for which it serves as foundation. 5. IANA Considerations This document has no IANA actions. 6. References 6.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC9421] Backman, A., Ed., Richer, J., Ed., and M. Sporny, "HTTP Message Signatures", RFC 9421, DOI 10.17487/RFC9421, February 2024, . 6.2. Informative References [FETCH] Kesteren, A. van., "Fetch Standard", n.d., . [I-D.pardue-http-identity-digest] Pardue, L., "HTTP Identity Digest", Work in Progress, Internet-Draft, draft-pardue-http-identity-digest-01, 7 March 2023, . [RFC4648] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 4648, DOI 10.17487/RFC4648, October 2006, . [SIGSRI] West, M., "Signature-based SRI", n.d.. [STRUCTURED-FIELDS] Nottingham, M. and P. Kamp, "Structured Field Values for HTTP", RFC 9651, DOI 10.17487/RFC9651, September 2024, . Acknowledgments TODO acknowledge. Author's Address Mike West Google, LLC. Email: mkwst@google.com